Hydrodesulfurization of selected gasoline fractions



H. D. NOLL May 9, 1961 HYDRODESULFURIZATION OF SELECTED GASOLINE FRACTIONS Filed Dec. 50, 1958 INVENTOR HENRY D. Nou.

ATTORNEY Henry D. Noll, Philadelphia, Pa., assignor to Houdry Process Corporation. Wilmin ton D of Delaware g el, a corporation Filed Dec. 30, 1958, Ser. No. 783,839

2 Claims. (Cl. 208-97) invention relatesto the treatment of crude oils having. a high sulfur content, and particularly to the ilrydrodesulfurization of gasoline fractions obtained thereom. t It is wellrecognized in the petroleum refining art that the presence of sulfur is objectionable in petroleum prod ucts generally, and is especially undesirable in motor 'fuels, such as gasoline, because of its characteristic of impairing the lead response for octane improvement. Furthermore, it has a tendency to form S which is both obnoxious and corrosive.

- 1 With respect to the hydrodesulfurization of catalytically-cracked gasolines, it has been found necessary to avoid an excessive loss of octane number in reducing the sulfur content to acceptable levels, particularly as a result of olefin saturation. One way in which this has heretofore been accomplished is by selective hydrodesulfurization over particular catalysts under selected conditions with respect to temperature, pressure, space rate and hydrogen-to-oil ratios.

Contained within the catalytically cracked gasoline, however, there are low-boiling olefinic components which readily become saturated under the conditions necessary for removal of those sulfur compounds which are more diificult to remove. It is known that improved hydrodesulfurization may be obtained by subjecting the catalytically-cracked gasoline to fractionation into lowerboiling and higher-boiling fractions, the cut being made in such manner that the former fraction will contain most of the olefins of the gasoline and few sulfur compounds, while the latter will contain relatively few olefins and most of the sulfur compounds. The higher-boiling fraction may then be subjected to hydrodesulfurization treatment at more severe conditions, since it contains relatively few olefins, and the lower-boiling fraction may either not be treated at all or, if its sulfur content is too high, be subjected to hydrodesulfurization treatment at very mild conditions so as to cause a minimum of olefin-saturation. The two gasoline fractions are then combined to form a gasoline of acceptable sulfur content with a minimum F-l clear octane loss due to olefin saturation, and often with an actual gain in F-l leaded octane for the same lead concentration.

With the development of new refinery processing techconditions.

In accordance with the present invention, a crude charge stock known to be relatively high in sulfur con- H United States Patent 0 r 2,983,669, Patented May 9, 1961 tent, such as a Wafra crude, is processed for maximum total recovery of high octane gasoline suitable for blending into refinery pools by heating to appropriate temperature and subjecting the heated material to a flash separation in order to obtain a lower-boiling straightrun products fraction comprising straight-run gasoline, kerosine and diesel oil and a remaining higher-boiling fraction, generally referred to as topped crude. The light, or low-boiling, fraction is relatively low in sulfur content, while the heavy, or high-boiling, fraction is relatively high in sulfur content.

The topped crude is then catalytically cracked-in known manner, and the product vapors are fractionated to produce a low-boiling overhead fraction comprising unstable, light, catalytically-cracked gasoline of low sulfur content, but rich in olefins, a naphtha fraction comprising catalytically-cracked naphtha of low sulfur content, a higherboiling distillate fraction of high sulfur content comprising catalytically-cracked kerosine and diesel oil and, of course, a bottoms fraction comprising heavy gas oil.

The distillate fraction withdrawn from the fractionator is then combined with the low-boiling, straight-run products fraction resulting from the flash separation of the vaporized crude. Following suitable hydrogen addition, the total mixture is reheated and then subjected to vapor phase hydrodesulfurization treatment in the presence of a cobalt-molybdena-alumina catalyst and under relatively severe reaction conditions. Optionally, these two fractions may be treated individually in separate hydrodesulfurization reactors, under severity conditions suitable to the sulfur content of the particular fraction.

The reaction products of such hydrodesulfurization treatment are then cooled, and the normally gaseous products, including hydrogen and hydrogen sulfide are separated. The separated gaseous product is then freed of hydrogen sulfide in known manner and the sulfur-free gas may then be used as recycle gas, supplemented with fresh make-up hydrogen, if needed.

The liquid product of such separation is fractionated to recover a 275 F. E.P. straight-run gasoline substantially free of sulfur, a light gas overhead, and products heavier than gasoline. Although the gasoline is of relatively low octane, it is nevertheless suitable for blending.

The naphtha fraction of the catalytically-cracked, topped crude is vaporized and then subjected to a selective hydrodesulfnrization treatment similar to that employed for treatment of the straight-run gasoline fraction, but at substantially milder conditions, since the naphtha fraction has a low sulfur content. As before, the treater product is cooled and separated. The sulfur, as hydrogen sulfide, is removed in known manner, and hydrogencontaining gas is recovered for recycle purposes. Makeup hydrogen is added, if necessary.

The condensed liquid product of the second hydrodesulfurization treatment may then be stripped to remove a light gaseous overhead which may contain some remaining sulfur components, leaving a heavier liquid portion of desulfurized catalytically-cracked naphtha.

The unstable, light, catalytically-cracked gasoline, which is high in olefin content and low in sulfur content, is then treated in known manner to remove C -C., and lighter components and the remaining C and heavier components are combined with the catalytically-cracked naphtha to form a 385 F. E.P. catalytic gasoline of relatively high octane.

For a fuller understanding of the invention, reference may be had to the following description and claims, taken in connection with the accompanying drawing forming a part of this invention and showing a typical preferred embodiment thereof.

Referring to the drawing, wherein the general layout of a refinery is diagrammatically illustrated, with omisphase stream to :a separator or'flash drum 35.

slon of various pieces of apparatus not considered necessary to an understanding of the invention, the crude charge stock is supplied through conduit 10.

The charge is heated in furnace 11 and is then passed through conduit 12 to a crude flash tower 13. The over.- ead from t e sh t wer. i ha g ng hroug o duit 14, comprises a fraction composed 'of gasoline, kerosine anddiesel oil.

The topped crude is withdrawn as a bottoms product from flash tower 13 and is passed, through a line 15 to a catalytic cracking unit 16. The catalytically-cracked reactor efiiuent from unit 16 is passed through conduit 17 to a fractionating column 18, commonly referred to as a synthetic crude tower. a

The fractionator overhead, withdrawn through conduit 19 comprises all the light gaseous efliuent, together with anunstable, light, catalyticallyrcracked gasoline comprising about 75 wt. percent of, the total gasoline in the reactor'efliuent of the cracking unit 16.

Intermediate cuts of catalytically-cracked naphtha, cempr ing the remaining approximately 25. percent of the total gasoline, and adistillate comprising catalyticallycracked kerosine and diesel oil are withdrawn at the sides of the fractionator through conduits 21 and 22, respectively. The usual provisions for stripping and overhead reflux are. provided for these intermediate cuts. Likewise, an intermediate side stream may be withdrawn, cooled and returned to the tower as reflux. For the sake of simplicity, such side reflux operation is not illustrated. The fractionator bottoms portion is withdrawn through conduit 23 and disposed of as heavy gas oil, or fuel oil product.

The straight-run gasoline, kerosine and diesel .oil {fraction withdrawn from crude flash tower 13 through conduit 14 is cooled in known manner and is-passed to an accumulator or reflux drum 24, from which a fraction of the condensate is continuously returned throughcon- ,duit 25 to the tower 13 as reflux, while the remainder of the condensed overhead stream, containing straight-run gasoline, kerosine and diesel oil, and having a relatively low sulfur content, is passed into conduit 26 for conveyance to a furnace 27.

The distillate fraction withdrawn as a side stream from fractionator 18 through conduit 22, and having a relatively high sulfur content, is introduced into conduit 26 containing the straight-run products fraction of low sulfur content from flash tower 13. The stream flowing to furnace 27 will therefore have a sulfur content intermediate to that of the individual combining streams. As

the mixed stream flows through conduit 26 to furnace 27., hydrogen is added as part of a sulfur-free recycle gas stream supplied through conduit 28, from a source hereinafter to be described, or, if needed, as fresh make-up hydrogen supplied through conduit 29.

The mixture of straight-run and catalytically-crackcd hydrocarbons and hydrogen heated in furnace 2 7 is conveyed therefrom by conduit 31 intoja hydrodesulfuriza- The separated 'vaporous material, containing the sulfur as hydrogen sulfide, is passed from flash drum 35 through conduit 36 to a scrubber 37 of known design wherein the hydrogen is recovered for recycle purposes and discharged tillate products splitter or fraetionator 39, i Th igh warhead pr ducts 59m r c onatqr ar withdrawn through conduit 41, cooled to condense the gasoline fraction, and then passed into the separator or flash drum 42. The separated gaseous etfluent is sent to fuel gas supply through conduit 43, a portion of the condensed gasoline product is returned to fractionator 39 through conduit 44 as reflux, and the remaining straight-run gasoline is discharged through conduit 45.

A side out comprising kerosine and jet fuel is withdrawn from fractionator 39 through conduit 46, is stripped, and then cooled; and a lower side cut comprising diesel oil is withdrawn through conduit .47, is stripped, and then cooled. V

The bottoms fraction is withdrawn from fractionator 39 through conduit 48 and, after cooling, is sent to fuel oil storage. a

The light straight-run gasoline from conduit 45, either alone or in combination with the fraction from conduit 46, is then stabilized in known manner, to recover product straight-run gasoline having a275 F. E.P. i The light overhead product discharged from fraction, ator 18 through conduit 19 is cooled and passed tog separator, or flash drum 51. The separated gaseous eflluent is discharged through conduit 52, while.the liquid condensate, comprising an unstable, light, catalytically cracked gasoline is in part returned to fractionator 18 through conduit 53 as reflux, but in major part discharged through conduit 54. The wet gaseous effluent in conduit 52 and the light catalytic gasoline in conduit 54 are sub.- jected to conventional treatment for removal of ethane, 'methane and hydrogen, which go to fuel gas, and for removal of C and C hydrocarbons, which go to liquefied petroleum gas. Such treatment is diagrammatically .desig nated at 55..

The catalytically cracked naphtha withdrawn from freetionator 18 through conduit 21 is passed to aheater Sfi, As in the case of the straight-run gasoline, kerosene, and diesel oil stream passing through conduit 26, the stream in conduit 21 is supplied with recycle hydrogen from conduit 28 and with 'fresh make-up hydrogen," as needed, through conduit 57. a A From heater 56, the hydrogen-containing-naphtha stream is passed through conduit 58 to hydrodesulfuri zation re,

actor 59, containing a bed of cobalt-molybdena-alumina catalyst 61. The type of treatment carried out in reactor 59 is similar to that in reactor 32, except that milder conditions may be employed in reactor 59 because the treated material is relatively low in sulfur content. effluent from reactor 59 is withdrawn through conduit 62, cooled, and separated in separator or flash drum -63.

The separated gaseous material, containing sulfur hydrogen sulfide, is removed from flash drum 63 through conduit 64 and is introduced into conduit 36 leadingto that is withdrawn through conduit 68. The gasoline prod.

not from treater 55 is withdrawn through conduit 69 and is mixed with the gasoline product from stripper 66 'to form a 385 F. E.P. catalyticallyrcracked gasoline of relax tively high octane value, which is suitable for blending with the 275 F. E-P. straight-run gasoline in conduit 45 Describing a typical operation in accordance with the, invention, wherein all stated percentages will be based upon the crude, the charge stock-received through conduit 10, heated in furnace 11 and charged to the crude flash tower 13 is, for example, a Wafra crude, familiar to those engaged in oil refining operations. The specific charge of Wafra crude is found to contain about 3.84- tperc n o sul ur- 1 After cooling and returning the essence The flash tower overhead admitted into conduit 26 foi' conveyance to the hydrodesulfurization reactor 32 comprises the following components in the stated proportion: 6 vol. percent of 275 F. E.P. gasoline containing .09 wt. percent of sulfur, 9.5 vol. percent of kerosinecontaining .40 wt. percent of sulfur, and 19.5 vol. percent of diesel oil containing 1.90 wt. percent of sulfur.

The topped crude withdrawn from flash tower- 13, which is catalytically-cracked in cracking unit 16 and then fractionated in tower 18, yields, among other things 3.6 vol. percent of catalytically-cracked naphtha containing 1.20 wt. percent of sulfur and a catalytically-cracked distillate fraction comprising 3.2 vol. percent of kerosine containing 2.0 wt. percent of sulfur and 7.1 vol. percent of diesel oil containing 3.8 wt. percent of sulfur.

The catalytically-cracked distillate fraction is withdrawn from fractionating tower 18 and is conveyed through conduit 22 to conduit 26, where it joins the stream of flash tower overhead. Hydrogen-containing gas and/or hydrogen is supplied to conduit 26 in such amount as to provide therein a hydrogen/oil mol ratio of about 3 to 1, which amount may be expressed in terms of about 1950 s.c.f./bbl. The admixture is then heated and, in vaporized or partially vaporized state, is introduced into hydrodesulfurization reactor 32 at a space rate (vol. oil/hr./vol. cat.) in the order of about 2.0. The inlet temperature and pressure of reactor 32 are about 700 F. and 750 p.s.i.g., respectively.

The reaction products from reactor 32, recovered in the manner herein described, comprise fuel gas, H S, 6.0 vol. percent of 275 F. E.P. gasoline containing .01 wt. percent of sulfur, 12.6 vol. percent of kerosine containing .05 wt. percent of sulfur, 26.0 vol. percent of diesel oil containing .37 wt. percent of sulfur, and 0.9 vol. percent of fuel oil containing .67 wt. percent of sulfur.

The catalytically-cracked naphthafraction withdrawn from fractionating tower 18 through conduit 21 for conveyance to the selective hydrodesulfurization reactor 59 is likewise admixed with hydrogen-containing gas and/or hydrogen to provide a hydrogen/oil mol ratio of about 3 to 1. This admixture is then heated and in vapor phase is introduced into reactor 59 at a space rate vol. oil/hr./ vol. cat. in the order of about 2.0. The inlet temperature and pressure of reactor 59 are about 650 F. and 300 p.s.i.g., respectively.

The reaction products from reactor 59, recovered in the manner herein described, comprise fuel gas, H 8, and 3.6 vol. percent of catalytically-cracked naphtha containing .04 wt. percent of sulfur.

It is to be understood that the foregoing is illustrative of a single preferred operation in accordance with the invention and that the conditions maintained in both the hydrodesulfurization reactor 32 and the selective hydrodesulfurization reactor 59 may vary to some extent. Thus, it is contemplated that in reactor 32 the space rate may be in the range of 0.5 to 10, the inlet temperature may be in the range of 650-800 F., the pressure may be in the range of 600-1000 p.s.i.g., and the hydrogen/oil mol ratio may be in the range of 1/1 to 5/ 1. In reactor 59, the space rate may be in the range of 1.0 to 50, the temperature may be in the range of 500-750 F., the pressure may be in the range of 200-700 p.s.i.g., and, again, the hydrogen/ oil mol ratio may be in the range of 1/ 1 to 5/ 1.

By the method of this invention it is possible to process high-sulfur crude charge stocks for the recovery of useful petroleum products relatively free of sulfur. For the purpose of this invention a high-sulfur crude may be considered one containing sulfur in an amount equivalent to 1 to 5, or even greater, weight percent.

With respect to the recovery of gasoline as one of the useful end products of the process, the invention makes possible the recovery of straight-run and catalytic gasoline of low sulfur content and relatively high octane value. This is achieved primarily through the feature of separately hydrodesulfurizing selected portions of the flash separated and.patalytically-cracked materials under dif;- ferent severity conditions. Under this arrangement, it is possible to hydrodesulfurize under relatively mild conditions that portion of the sulfur-rich catalytic gasoline fraction which is mostsusceptible to undesirable hydrogenation of olefinic and aromatic constituents, whereby these constituents may be retained to the greatest possible extent, consistent with the necessary sulfur removal, for octane improvement and increased lead response in the ultimate gasoline product. Since hydrogenation of the hydrocarbons is to be minimized in the treatment of the catalytic gasoline fraction containing unsaturates readily susceptible to hydrogenation, not only may the reaction conditions be substantially milder in the reactor handling the latter fraction, but the catalyst may be one which does not too readily promote the hydrogenation reaction. Thus, it is possible to use in the latter reactor either a different catalyst or the same type of catalyst after it has become partially spent.

As an alternative to the arrangement of processing equipment herein described and illustrated, it is contemplated that the fraction of catalytically cracked material withdrawn from fractionator 18 through conduit 22 may be sent to a separate hydrodesulfurization reactor, instead of being combined with the material in conduit 26 and being treated in reactor 32. Also, that the gaseous materials withdrawn from separators 35 and 63 may be treated in separate units 37 for removal of sulfur instead of in a common unit as shown.

Obviously many modifications and variations of the in vention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

1. In a hydrocarbon conversion process for the treatment of a crude charge stock of high sulfur content, wherein said charge stock is initially separated into a low-boiling straight-run products fraction comprising straight-run gasoline, kerosene and diesel oil and a topped crude fraction and wherein said topped crude fraction is catalytically cracked and then fractionally distilled to recover a bottoms fraction comprising heavy gas oil and a catalytic products fraction consisting of the components boiling lower than said heavy gas oil, the method for removing sulfur from both said straight-run and catalytic products fractions preliminary to further treatment thereof for ultimate recovery of desired end products, which method comprises the steps of: further fractionating said catalytic products fraction to separate therefrom a naphtha fraction in the gasoline boiling range, leaving a gasolinefree distillate fraction of relatively high sulfur content including catalytically cracked kerosene and dieselv oil; combining said distillate and straight-run products fractions; adding hydrogen-containing gaseous material to said combined fractions in a hydrogen/oil mol ratio of between about 1/1-5/ 1 and subjecting the resultant mixture to relatively severe hydrodesulfurization treatment in the presence of cobalt-molybdena-alumina catalyst at a space rate in the range of about 0.5-l0, at a vapor inlet temperature of about 600-800" F. and at a pressure of about 600-1000 p.s.i.g.; cooling the effiuent of said hydrodesulfurization treatment and removing therefrom gaseous products containing hydrogen sulfide, thereby obtaining for said further treatment a desulfurized. liquid product comprising straight-run naphtha, kerosene and diesel oil.

2. In a hydrocarbon conversion process for the treatment of a crude charge stock of high sulfur content,

'wherein said charge stock is initially separated into a .mnts bOilinglDWet than said heavy gasloil, a method for refining said catalytic products fraction which comprises the stepsof: further fractionating said. catalytic products fraction into a light gasoline. fraction, containing the major portion of the total catalytic gasoline, and a heavy catalytic gasoline fraction of relatively low sulfur content, leaving a gasoline-free distillate fraction of relatively high sulfur content including catalytically cracked kerosene and diesel, oil; adding hydrogen-containing gaseous material to said heavy catalytic gasoline fraction in a hydrogen/oil mol ratio of between 1/1-5/1 and subjecting the gaseous material-gasoline fraction to relatively mild hydrodesulfurization treatment. in the presence. of cobaltmolybdena-alumina catalyst at a space rate, in the range -8 of about 1.0-50, at. avapor inlet. temperature vof about 500-750 F; and at. apressure of about200-700 p.s,i.g.; cooling the effiuentjof said, hydrodesulfurization treatment and removing therefrom, gaseousproducts containing hydrogen sulfide, thereby obtaining, a d'esulfurized liquid product comprising heavy catalytically-cracked gasoline.

References Cited, inthe'file of, patent UNITED STATES PATENTS 

1. IN A HYDROCARBON CONVERSION PROCESS FOR THE TREATMENT OF A CRUDE CHARGE STOCK OF HIGH SULFUR CONTENT, WHEREIN SAID CHARGE STOCK IS INTIALLY SEPARATED INTO A LOW-BOILING STRAIGHT-RUN PRODUCTS FRACTION COMPRISING STRAIGHT-RUN GASOLINE, KEROSENE AND DIESEL OIL AND A TOPPED CRUDE FRACTION AND WHEREIN SAID TOPPED CRUDE FRACTION IS CATALYSTICALLY CRACKED AND THEN FRACTIONALLY DISTALLED TO RECOVER A BOTTOMS FRACTION COMPRISING HEAVY GAS OIL AND A CATALYTIC PRODUCTS FRACTION CONSISTING OF THE COMPONENTS BOILING LOWER THAN SAID HEAVY GAS OIL, THE METHOD FOR REMOVING SULFUR FROM BOTH SAID STRAIGHT-RUN AND CATALYTIC PRODUCTS FRACTIONS PRELIMINARY TO FURTHER TREATMENT THEREOF FOR ULTIMATE RECOVERY OF DESIRED END PRODUCTS, WHICH METHOD COMPRISES THE STEP OF: FURTHER FRACTIONATING SAID CATALYTIC PRODUCTS FRACTION TO SEPARATE THEREFORM A NAPHTHA FRACTION IN THE GASOLINE BOILING RANGE, LEAVING A GASOLINEFREE DISTILLATE FRACTION OF RELATIVELY HIGH SULFUR CONTENT INCLUDING CATALYTICALY CRACKED KEROSENE AND DIESEL OIL; COMBINING SAID DISTILLATE AND STRAIGHT-RUN PRODUCTS FRACTIONS ADDING HYDROGEN-CONTAINING GASEOUS MATERIAL TO SAID COMBINED FRACTIONS IN A HYDROGEN/OIL MOL RATIO OF BETWEEN ABOUT 1/1-5/1 AND SUBJECTING THE RESULTANT MIXTURE TO RELATIVELY SEVERE HYDRODESULFURIZATION TREATMENT IN THE PRESENCE OF COBALT-MOLYBDENA-ALUMINA CATALYST AT A SPACE RATE IN THE RANGE OF ABOUT 0.5-10, AT A VAPOR INLET TEMPERATURE OF ABOUT 600-800*F. AND AT A PRESSURE OF ABOUT 600-1000 P.S.I.G.; COOLING THE EFFLUENT OF SAID HYDRODESULFURIZATION TREATMENT AND REMOVING THEREFROM GASEOUS PRODUCTS CONTAINING HYDROGEN SULFIDE, THEREBY OBTAINING FOR SAID FURTHER TREATMENT A DESULFURIZED LIQUID PRODUCT COMPRISING STRAIGHT-RUN NAPHTHA, KEROSENE AND DIESEL OIL. 